Small arms locator



F. P. JOHNSON 3,445,808

SMALL ARMS LOCATOR May 20, 1969 Filed April 5, 1968 zi .1 I fe, @gw YATTORNEYJ.

United States Patent O 3,445,808 SMALL ARMS LOCATOR Fred P. Johnson,Pittsfield, Mass., assignor, by mesne assignments, to the United Statesof America as represented by the Secretary of the Army Filed Apr. 5,1968, Ser. No. 719,137 Int. Cl. G01s 3/ 80 U.S. Cl. 340-16 5 ClaimsABSTRACT F THE DISCLOSURE The direction of a bullet is ascertained bycomparing the points at which it passed through two planes. Each pointis pinpointed instantly by comparing the time element required for asound, generated as the bullet passes through the plane, to reachvarious microphones at preselected points in each plane.

BRIEF SUMMARY Direction finders, comprising audio sensors, microphonesor other energy sensors, have been used in various groupings to indicatethe direction of a source of sound or energy generator. However, suchdirection finders have enjoyed only limited utility. In a given setting,such as in a battle, many sounds may be generated simultaneously, suchas guns tiring, projectiles exploding, etc., thereby making itimpossible or diicult to isolate a particular sound-source. Perhaps onlyone gun has found its target (your helicopter) and that gun should bepinpointed instantly for counterfire purposes or evasive action.

This invention helps pinpoint the direction from which came an objectthat has found its mark and scored a hit.

IN THE DRAWING FIGURE 1 is a diagrammatic illustration of the timedifferential principles involved;

FIGURE 2 is a diagrammatic illustration of the path a bullet passingthrough two planar sound-producing objects;

FIGURE 3 is a block-diagram of the computer system of the invention.

DETAILED DESCRIPTION Sensors 1, 2, 3 and 4 are placed at predeterminedlocations relative to a substantially planar object or sheet 5. Asexemplary, four sensors, more or less, may be audio sensors ormicrophones and the sheet may be rectangular, four by eight feet.

An object, such as a bullet, strikes sheet 5 at point P and generatesconcentric sound waves progressing toward the sensors. The sound reachesthe sensors at the same instant only if the bullet struck the center ofthe sheet. Otherwise, the time of arrival of the sound at the varioussensors is different. A difference in the time of sound arrival atsensors 1 and 2 can be expressed as This time difference, A114, willnot, by itself, locate the point of peneration P. It will describe alocus of points, hyperbola H1 2, that will contain the point P. The timedifference between sensors 2 and 3 will describe a second locus ofpoints, hyperbola H2 3, that will intersect H1 2 3,445,808 Patented May20, 1969 ICC at P. Time data from sensor combination 3-4 and 4-1 can beused to correlate this location.

In FIGURE 2 two spaced apart sheets 5 and 5"-are illustrated. Sheet 5has sensors 1 to 4 at its corners corresponding with `sensors 1 to 4 atthe corners of sheet 5. These sheets should preferably be parallel tosimplify computations. The bullet 6 penetrates these sheets at points Pand P. A straight line interconnecting these points, when traced back tothe ground or jungle below, indicates approximately where the bulletcame from.

FIGURE 3 indicates the well-known pieces of electronic equipment used tobring out the desired data from the equipment described above. Thesounds from the bullet are detected by the sensors 1-4 and 1'4'. Theoutput of the senors is fed into computer means including the output ofclock 7, threshold gate 8, counter 9 and computer 10. Computer 10 alsomay receive data as to vehicle (helicopter) speed, heading, altitude andvertical reference. The computer may correlate the data fed thereintoand computes the gun location data so that the pilot or gunner canpinpoint the gun position instantly for evasive or counterfire action.Theoretically it should be possible to feed the gun location datadirectly into gun control equipment on the vehicle which wouldautomatically train the vehicle gun on the gun position from which thebullet came and quickly initiate counterfire. However, such system goesbeyond the scope of the present system.

Sheets 5 and 5' are shown for purposes of illustration of the principlesinvolved. These sheets may be separate elements carried by a vehicle. Ofcourse they may be used in the area of a stationary gun emplacement onthe ground. In such installation the sheets could be placed in verticalplanes so that a projectile coming in on a nearhorizontal path wouldpenetrate the sheets successively and the invention would pinpointsniper or enemy gunlire ahead as it comes dangerously close.

In some installations there need be no separate sheets as such. Forexample, in a plane or helicopter, the skin of the craft, when piercedby `a bullet, will generate the sounds as it passes through the bellyand the top of the craft. Microphones, properly positioned relative tothese parts of the skin of the craft, will detect the sounds aspreviously described.

I claim:

1. The method of determining the direction of a passing objectcomprising placing a first plurality of energy sensors at preselectedpoints substantially in a rst plane, placing a first substantiallyplanar object substantially in said first plane, placing a secondplurality of energy sensors substantially in a second plane, placing asecond substantially planar object substantially in said second plane,using said first sensor to determine the location at which said passingobject passed through said iirst plane, using said first sensors todetermine the location at which said passing object passed through saidsecond plane, and comparing the locations in the planes to determine thedirection ofthe passing object.

2. Apparatus for determining the direction of a passing objectcomprising a first plurality of energy sensors placed at preselectedpoints substantially in a first plane, a first substantially planarobject substantially in said first plane, a second plurality of energysensors substantially in a second plane, a second substantially planarobject substantially in said second plane, computer means con- 3 tnected to said first sensors and said second sensors to indicate thelocation of said passing object as it passes through said rst and secondplanes and to compare the locations to thereby determine the directionof the passing object.

3. Apparatus as in claim 2 wherein said energy sensors comprisemicrophones, sensitive to energy waves generated as said passing objectpasses through said planar objects.

4. Apparatus as in claim 3 wherein said energy sensors comprise fourmicrophones, substantially in each plane, substantially at the cornersof a pair of rectangles.

l4 5. Apparatus as in claim 2 wherein said first and second planes aresubstantially parallel.

References Cited UNITED STATES PATENTS RICHARD A. FARLEY, PrimaryExaminer.

U.S. C1. X.R. ISI-.5; 340-6 22253310 UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Patent No. 3,445,808 Dated 2O May 1969Inventor(s) FRED P. JOHNSON It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 2, line 53, "sensor" should be sensors Column 2, line 55, "first"should be second SIGNED AND SEALED SEP 2 1959 (SEAL) Attest:

ard Edw M Flecher Ir WILLIAM E SCIHUYLER, JR- Attestmg Offlcercommissioner of Patents

